The invention relates to a patch antenna, in particular for the microwave range, with at least one patch resonator with a metal patch pattern and a ground metallization as well as a feed terminal for the supply of electromagnetic energy.
Electromagnetic waves in the microwave region are used in mobile telecommunication for the transmission of information. Examples of this are the GSM mobile telephone standard in the frequency range from 890 to 960 MHz (GSM900) and from 1710 to 1880 MHz (GSM1800 or DCS), furthermore the UMTS band (1970 to 2170 MHz), the DECT standard for cordless telephones in the frequency range from 1880 to 1900 MHz, and the new Bluetooth standard in the frequency range from 2400 to 2480 MHz, which serves to exchange data between, for example, mobile telephones and other electronic devices such as, for example, computers, other mobile telephones, etc.
The market shows a strong trend towards miniaturization of these devices. This results in the wish also to reduce the components for the mobile communication, i.e. the electronic components, in size. The antenna types used at present in mobile telephones, which are usually wire antennas, have substantial disadvantages in this respect, because they are comparatively large. They project from the mobile telephones, may readily break off, may come into undesirable eye contact with the user, and also stand in the way of an aesthetic design. Increasingly, moreover, an undesirable microwave irradiation of the user by the mobile telephone has become a subject of public discussion. A major portion of the emitted radiation power may be absorbed in the user""s head in the case of wire antennas which project from the mobile telephone.
A further problem arises from the fact that surface mounting (with SMDs or surface mounted devices), i.e. the planar soldering of electronic components onto a PCB or printed circuit board by means of a wave soldering bath or a reflow soldering process, has become common practice in the technical realization of modern digital electronic devices. The antennas used until now, however, are not suitable for this mounting technology, because they often can only be provided on the printed circuit board of the mobile telephone by means of special supports, while also the supply of electromagnetic power is only possible by means of special supply/support members such as pins or the like. This causes undesirable mounting steps, quality problems, and additional expense.
The antennas used nowadays in mobile telephones radiate electromagnetic energy upon the creation of an electromagnetic resonance. This requires that the length of the antenna should at least be equal to one fourth the wavelength of the transmitted radiation. With air as the dielectric (∈r=1), this results in a necessary antenna length of 75 mm for a frequency of 1 GHz.
To minimize the size of the antenna for a given wavelength of the emitted radiation, a dielectric with a dielectric constant ∈r greater than 1 may be used as a basic building block for the antenna. This leads to a reduction in the wavelength of the radiation in the dielectric by a factor 1/⊂∈r,. An antenna designed on the basis of such a dielectric will accordingly have its size reduced by this same factor.
The so-called patch pattern antenna or patch antenna as described, for example, in WO 98/18177, is an antenna type in which the miniaturization by means of the dielectric constant ∈r can be utilized. It consists of a solid block of dielectric material with ∈r greater than 1. The height of the block here typically is smaller than its length and width by a factor 3 to 10. The block is provided with a pattern of metal patches over the whole or part of one surface, and with a ground metallization on the other surface. Between these electrodes, electromagnetic resonances are generated whose frequencies depend on the dimensions of the electrodes and the value of the dielectric constant ∈r of the block. The values of the individual resonance frequencies decrease with increasing lateral dimensions of the antenna andxe2x80x94as described abovexe2x80x94with increasing values of the dielectric constant ∈r. To achieve a high degree of miniaturization of the antenna, therefore, ∈r will be designed to be high, and the mode having the lowest frequency will be chosen from the resonance spectrum. This mode is denoted the base or fundamental mode.
A step towards further miniaturization consists in the additional insertion of a conductive connection (short-circuit conductor) in the dielectric between the two electrodes. Given a same resonance frequency, it is usually possible to reduce the size of the antenna by a factor 4 thereby.
A problem in these patch antennas (with or without short-circuit conductor) is, however, that the bandwidths amount to only a few MHz for the resonance frequencies lying within the frequency range of the GSM standard. In addition, the bandwidth decreases as the dielectric constant ∈r of the dielectric material increases. The bandwidth required for the GSM standard by contrast is approximately 70 MHz. Conventional patch antennas are accordingly unsuitable for such broadband applications.
Several patch pattern resonators with or without short-circuit conductors may be vertically stacked so as to realize greater bandwidths also with patch antennas. This configuration is denoted a multilayer patch antenna. The number of fundamental modes of the multilayer patch antenna is equal to the number of constituent patch resonators. If the frequency distance between the fundamental modes is smaller than the bandwidth thereof, the total bandwidth of the antenna can thus be increased.
This type of antenna, however, also has two major disadvantages. On the one hand, substrate materials with dielectric constant values which can be easily distinguished must be used (for example ∈r1=2.2 and ∈r2=1.07) for the individual patch resonators so as to achieve a suitable frequency distance of the resonators. This increases the manufacturing expenditure.
On the other hand, a coax cable was found to be the only means for supplying the antenna with electromagnetic power and for adjusting the input impedance of the antenna over a limited range such that only small reflections occur at the feed structure in the case of multilayer patch antennas with short-circuit conductors. This type of feedline, however, hampers an SMD integration on a printed circuit board (PCB) of a mobile telephone, because suitable pins are to be provided for the supply of the electromagnetic power on the PCB which are to be passed through the metallization from below, so that the antenna cannot be soldered on the PCB together with the other components by means of surface mounting (SMD technology).
It is accordingly an object of the invention to provide a patch antenna of the kind mentioned in the opening paragraph which is suitable for surface mounting (SMD) on a printed circuit board, also with a short-circuit conductor.
It is also an object of the invention to provide a patch antenna which with small dimensions provides a bandwidth satisfactory for the applications mentioned above, also without the use of dielectrics which have different dielectric constants.
Furthermore, the invention is to provide a patch antenna whose input impedance can be adjusted such that the power supplied to the antenna is not reflected at the antenna but is substantially completely radiated without the antenna having to comprise a coaxial feed line.
Finally, a patch antenna is to be provided which has as a feature a particularly great bandwidth.
According to claim 1, these objects are achieved by means of a patch antenna of the kind mentioned in the opening paragraph which is characterized in that the feed terminal comprises at least a first metallization piece which extends over a first side face of the resonator between the ground metallization and the pattern of metal patches, while the input impedance of the antenna is determined by the dimensions of said metallization piece.
A particular advantage of this solution is that an optimum attunement of the input impedance to a concrete constructional situation is possible in a simple manner (for example through laser trimming), so that no reflections occur at the antenna and the supplied electromagnetic power is substantially fully radiated. This antenna may at the same time be fitted with a short-circuit conductor for reducing its dimensions.
A further solution to the problems mentioned above is achieved with a patch antenna of the kind mentioned in the opening paragraph according to claim 4, which is characterized by a line resonator which is formed by a line provided on at least a substrate and which serves for a resonant coupling of the electromagnetic energy supplied to the feed terminal into the at least one patch resonator.
A particular advantage of this solution is that this resonant coupling mechanism does not detract from the formation of the patch pattern resonances, and the bandwidth of the antenna can be further increased to a substantial degree through the addition of a further resonance. In addition, this antenna is also suitable for SMD mounting and for the provision of a short-circuit conductor.
The dependent claims relate to advantageous further embodiments of the invention.
The embodiment of claim 2 enables a particularly simple surface mounting of the antenna by the SMD technology because the second metallization piece can be directly soldered together with the ground metallization onto a printed circuit board.
The embodiment of claim 3 has the particular advantage that the bandwidth is further increased through the two resonators, also when substrates of the same dielectric or permeability value are used, and that it is also suitable for a construction with a short-circuit conductor.
The embodiment of claim 5 has the particular advantage that the coupling strength between the line resonator and the patch resonator can be adjusted by means of the dimensions of the end portion. A farther advantage of this embodiment and of that defined in claim 7 is that the frequency of the resonant coupling can be adjusted through suitable definitions of the lengths of said lines.
The embodiment of claim 6 renders possible an adaptation of the coupling strength between the feed terminal and the line resonator.
The bandwidth of the antenna can be further increased with the embodiment of claim 8, while the embodiments of claims 9 and 10 essentially enable a further miniaturization of the antenna.
The antenna according to the invention, finally, may be used to particular advantage on a printed circuit board as defined in claim 11 and in a mobile telecommunication device as defined in claim 12.